An invention patent application for a safety syringe, filed by the same inventor of this application on Nov. 30, 1992 given a Ser. No. of 07/983,144, includes: a hollow needle (2) preliminarily held in a rigid blocking disk (4) embedded in a rear disk socket (135) perpendicularly formed in a flexible plug (13) inserted in a front portion of the syringe (1) for injection use having a needle head portion (23) formed on a rear portion of the needle (2), and a plunger (31) slidably held in the syringe (1) for boosting a liquid medicine in the syringe to be injected into a patient through the hollow needle (2) having a needle-head socket (32) recessed in the plunger (31) to be engageable with the needle head portion (23) for pushing the needle head portion of the needle (2) frontwardly to drive the rigid blocking disk (4) frontwardly to engage the blocking disk (4) into a front disk socket (137) which is normally inclinedly formed in the flexible plug (13), whereby upon a retraction of the plunger (31) and the needle (2) with the needle head portion (23) received in and coupled to the plunger (31) into the syringe (1) to disengage the needle (2) from the rigid disk (4), the flexible plug (13) will restore the front socket (137) and the rigid disk (4) embedded in the front socket (137) to be inclinedly positioned in the plug (13), thereby blocking an outward protruding of the needle (2) retracted in the syringe (1) for preventing its injury or infectious contamination to the surroundings.
However, the blocking disk member 4 of this earlier application is made as a shallow disk, the central through hole 41 of the block disk member 4 can only be biased for a small oblique angle, which may still be accidentally inserted by an outwardly protruding of the needle (2) already retracted in the syringe (1) to lose its safety meaning.
Meanwhile, the hollow needle (2) of such a safety syringe is normally provided in a central portion of the syringe means (1), which is suitable for hypodermic or intramuscular injection. However, if such a syringe is used for intravenous or intravascular injection of larger quantity of liquid medicine filled in the syringe cylinder (11) such as a volume of 30 cc, 50 cc, or 100 cc of the liquid medicine. The needle (2) should be eccentrically formed in the syringe cylinder for an ergonomic injection by a nurse or a doctor since the needle and the syringe cylinder can be held in a direction parallel and close to the patient's vein or blood vessels.
If the inventor's earlier application (U.S. patent application Ser. No. 07/983,144) is inferentially used for an intravenous injection of larger injection quantity, the needle (2) should be eccentrically mounted in the syringe cylinder (11). Meanwhile, the single needle-head socket (32) should also be eccentrically moved in order to engage with the needle head portion (23) of the needle (2). It will be very difficult and inconvenient for matching a needle head portion (23) of an eccentrically-positioned needle (2) with the single needle-head socket (32).
It is therefore expected to disclose a syringe for improving the drawbacks of the applicant's earlier application in order that a used needle can be easily retractable into the syringe in a safer way for preventing an outward protruding of the retracted needle.